Four days before our Citizens Police Academy class on drunken driving Tuesday night, one of our classmates, Kensington resident Dan Bushman, experienced a drunken driver firsthand on his ride-along with a county police officer.

"Seriously, she's lucky that she didn't kill somebody," he said, remembering how intoxicated the woman was Saturday night. "She was incredibly [drunk]."

Just after 8 p.m., Bushman and his ride-along officer were dispatched to the Glen Echo Volunteer Fire Station on Massachusetts Avenue in Bethesda to meet a driver who had been waiting at a red light when a dark vehicle slammed into him from behind and quickly fled the scene.

Thanks to a witness who provided the car's license plate, the officer and Bushman tracked the vehicle to a nearby residence where they found the driver, unconscious and clearly inebriated.

"She didn't really know where she was, what she was doing or anything," Bushman said. "She was in her own little world."

Because he witnessed the incident, Bushman will likely appear in court to testify before a judge, he said. He has already provided the department with a written report of what he saw.

The scenario, unfortunately, gets played out thousands of times in the county each year, according to Officer Chester Phillips of the department's Alcohol Enforcement Unit.

Officers adhere to a strict set of criteria before determining if a driver is either driving while impaired (DWI) or driving under the influence (DUI). A driver with a blood alcohol concentration (BAC) of .07 percent is guilty of a DWI, while .08 percent or more will be ruled a DUI and subject to harsher penalties.

"You don't have to act drunk to be arrested for DUI," Phillips said, explaining that arrests are made based on field sobriety tests and breath/alcohol test machines that determine a driver's BAC.

Later, Phillips and fellow Officer Rick Burge of the alcohol unit showed the class how officers determine a driver's BAC using three field sobriety tests. Two volunteers, an off-duty county sheriff and Steve Casey, a volunteer firefighter, were brought in after being given several drinks in another room.

Burge first had Casey follow a pen with his eyes as he moved it back and forth in front of his face. Officers look for slight trembling in the pupils, called "retina nystagmus." The twitching usually occurs involuntarily when a person with high BAC is made to look at a 45-degree angle, Burge said.

The standard "walk and turn" and "stand on one foot" tests were also administered.

"You see how he kind of slipped there?" Burge asked the class as Casey did his best to pass the walking test.

"But I haven't had anything to drink!" Casey protested at one point with a crooked grin.

A subsequent breath test put Casey at .14 BAC, well over the legal limit. Burge drove both volunteers home following the class.

Join us next week for a grave discussion with county police Forensic Service professionals and watch CSI come to life with a lecture by Crime Lab representatives.